Process for the production of a steering wheel for a motor vehicle

ABSTRACT

A procedure for the manufacture of a steering wheel for motor vehicles consisting of an outer covering in composite material, comprising the preparation of the covering by means of composite elements with a laminar structure, the hot forming of these elements in order to obtain a pair of complementary shells ( 13   a,    13   b ), the assembly of the shells on the opposite sides of the steering wheel, in which the body of the steering wheel consists of a metal core ( 11 ) buried inside synthetic resin, and in that at least one of the shells forming the opposite sides of the covering is equipped with a support element ( 14   a,    14   b ) which allows it to be coupled to the other shell complementary to it.

TECHNICAL FIELD

This invention refers to a procedure for the manufacture of a steeringwheel for motor vehicles consisting of an external covering in compositematerial.

More in particular, this invention refers to a procedure which comprisesthe preparation of composite elements with a laminar structure, hotforming of the elements to obtain a pair of shells, each having a shapecorresponding to half of the steering wheel to be produced, and assemblyof the shells on the opposite sides of the steering wheel, the body ofthe steering wheel consisting of a metal core buried inside syntheticresin.

BACKGROUND ART

It is known that steering wheels for motor vehicles can consist of astructure that comprises a metal core buried inside synthetic resin, andan outer covering consisting, for example, of a bivalve shell whichforms the part designed to be gripped and the external appearance of thesteering wheel.

One of the various procedures employed in the manufacture of steeringwheels for motor vehicles uses two shells to form the outer covering,obtained by hot forming of suitable laminar material.

After the edges have been finished by means of mechanical machining, theshells are respectively applied to the opposite sides of the steeringwheel consisting of the metal core and the synthetic resin covering.

The two shells making up the covering are then fixed to each other onthe steering wheel by means of gluing along their contact line.

The gluing of these shells often proves to be a key step in theproduction process as a whole, particularly because the thickness of theshells is minimal, generally a few tenths of a millimeter.

Some solutions are known to the background art that would tend to makethe gluing of the shells more resistant; one example is described in thepatent application EP-A1-1029770 where the edges of the shells formingthe covering are mechanically machined in such a way to obtain a malefemale type complementary joint that couples together when the twoshells are applied to the body of the steering wheel.

The solution proposed by the previous patent clearly tends to increasethe contact surface along the edge of the shells so as to improve thefixing and the gluing.

The solution presented by the patent application EP-A1-1029770 isinevitably insufficient and difficult to apply when the thickness of theshells is minimal and not easy to machine; in fact the shells often tendto break and to develop cracks during the mechanical machining of theedges to form the coupling surfaces.

A further typical example in which the gluing problem becomes evident iswhen carbon fibre shells are used.

In the patent application EP-A1-1029771 the fixing phase of the twoshells on the body of the steering wheel comprises a previous stage inwhich the support sections are applied and fixed on the synthetic resinbody of the steering wheel.

These sections are shaped to form a base for the support and fixing ofthe two shells.

In practice the sections are normally made of metal, typically aluminumwhich permits easy clinching to the body of the steering wheel and aparticular aesthetic appearance when the section is left on view asdescribed in the patent application EP-A1-1029771.

On the other hand, however, the use of metal material is particularlydisadvantageous in consideration of the great difference in thecoefficient of thermal expansion of these materials compared with thematerials used to manufacture the coverings.

In fact, as the steering wheels of motor vehicles are subject to hightemperature ranges the great difference in the coefficient of thermalexpansion of these materials inevitably leads to the two shells formingthe outer covering becoming detached.

In addition to the aforesaid drawback, the procedure described in thepatent EP-A1-1029771 presents a further disadvantage in consideration ofthe particular machining that the body of the steering wheel mustundergo.

The gluing or clinching of the sections must in fact be carried out withparticular precision so as to avoid problems when fitting the shells onthe body of the steering wheel and the unsightly appearance of the endproduct.

Document WO-A2-0005123 describes a steering wheel comprising adecorative covering especially with decorative wood. The steering wheelframe is provided with a foam sheathing in the area (3, 4) which areprovided for the decorative covering and which comprise outer dimensionsthat are smaller than those of the remaining areas. Furthermore, theabove document describes that one dimensionally stable decorativecovering part is fastened on said foam sheathing and at least onecentering means is provided between the foam and the decorative coveringpart.

The procedure for manfacturing a steering wheel according to documentWO-A2-0005123 requires the centering of at least one of the shells onthe body of the steering wheel and furthermore the gluing involve notonly the shells but also the body of the steering wheel. These areclearly strong drawbacks since the deformations of the material due tothe high variance of the temperatures inside the car cause an alterationin the stability of the steering wheel.

DESCRIPTION OF THE INVENTION

The present invention aims to overcome the drawbacks comprised in thebackground art by means of a procedure that comprises the preparation ofcomposite elements with a laminar structure, hot forming of the elementsto obtain a pair of shells, each having a shape corresponding to half ofthe steering wheel to be produced, and assembly of the shells on theopposite sides of the steering wheel, the body of the steering wheelconsisting of a metal core buried inside synthetic resin.

This is achieved by means of a procedure with the features described inthe main claim.

The dependent claims describe advantageous embodiments of the invention.

The procedure according to the present invention comprises a phase,carried out before assembly on the body of the steering wheel, in whichthe shells are fitted on internal elements designed to ensure effectiveand long-lasting gluing both to the steering wheel and between the twoshells comprising the covering.

According to a particularly advantageous form of embodiment of theinvention, after mechanical finishing of the relative edges an elementwith the structure of a particularly thin shell, and a widercross-section than the shell to which it is applied and which will formthe outer covering of the steering wheel, is glued inside a first shellcomprising the covering and obtained by hot forming.

The second shell comprising the covering is fitted over the projectionsof the inner shell applied to the first shell, being fixed by gluing.

According to a particularly advantageous form of embodiment of theinvention, an element with the structure of a particularly thin secondshell, and a smaller cross-section than the shell to which it isapplied, is fixed inside both shells forming the covering of thesteering wheel.

In this case, the elements are applied displaced with respect to theedges of the shells so that one of the edges of the applied elementprojects slightly with respect to the edge of one of the shells.

Two shells are thus obtained and used to form the covering of a steeringwheel for motor vehicles, having a structure at their respective edgeswhich is very similar to a male female joint structure obtained withoutany specific machining of the edges, a process which would beparticularly delicate in view of the minimal thickness of the shells.

This particular form of embodiment according to the invention also makesit possible to guarantee support and reinforcement of the shells makingup the covering of the steering wheel and in the assembly stage todistribute any elastic stress on both parts of the structure and notsolely on one of the two as in the previous form of embodiment.

According to another form of embodiment of the invention, the elementsapplied to the shells forming the covering of the steering wheel consistof flat plates with an elongated structure.

These elements are applied to the edges of the shells to create thecoupling system as for the previously described form of embodiment.

ILLUSTRATION OF THE DRAWINGS

Other features and advantages of the invention will become evident onreading the following description of some forms of embodiment of theinvention, given as nonbinding examples, with the help of the encloseddrawings, in which:

FIG. 1 represents, in largely schematic form, a first embodiment of aprocedure for the manufacture of a steering wheel for motor vehiclesaccording to the present invention;

FIG. 2 represents, in largely schematic form, a second embodiment of aprocedure for the manufacture of a steering wheel for motor vehiclesaccording to the present invention;

FIG. 3 represents, in largely schematic form, a third embodiment of aprocedure for the manufacture of a steering wheel for motor vehiclesaccording to the present invention;

FIGS. 4 and 5 represent two respective cross sections of a steeringwheel for motor vehicles manufactured by means of two forms ofembodiment of the procedure according to the present invention.

DESCRIPTION OF SOME FORMS OF EMBODIMENT

A classic steering wheel for motor vehicles normally comprises a centralpart or hub, a plurality of radial spokes and an outer edge.

As is known from forms of embodiment comprised in the background art,the outer edge 10 consists of a metal core 11 buried inside syntheticresin 12.

This is all enclosed in an outer casing consisting for example of acovering 13.

This covering 13 generally consists of two shells 13 a, 13 bsuperimposed one on the other and joined together.

These shells 13 a, 13 b may be produced for example by means of theforming of glass fibre or carbon fibre materials with a laminarstructure according to known procedures and additionally treated andmachined in order to provide the structure with features of rigidity andgripping stability.

The shells obtained by means of these machining processes, as shown inFIGS. 1 to 3, comprise a convex external side, a concave internal sideand edges.

According to a first form of embodiment of the present invention, shownin FIG. 1, elements 14 a, 14 b which may be made from composite materialare applied to the inner side of the shells 13 a, 13 b and constitutethe system which connects and fixes the two shells 13 a, 13 b formingthe covering 13.

According to a second form of embodiment of the present invention, shownin FIGS. 2 and 4, a similar element 14 is applied to the inner side ofthe shell 13 a in such a way that the edges of this element 14 projectwith respect to the edges of the shell 13 a and can couple and be joinedfor example by means of gluing to the edges of the second shell 13 bforming the covering of the steering wheel

According to a third form of embodiment of the present invention, shownin FIGS. 3 and 5, an element 14 a, 14 b is applied to the inner side ofboth shells 13 a and 13 b near a respective edge in such a way that theedges of this element 14 project with respect to the edges of the shell13 a and can couple and be joined for example by means of gluing to theedges of the second shell 13 b forming the covering of the steeringwheel.

The elements 14 a and 14 b applied to the shells 13 a and 13 b formingthe covering of the steering wheel consist in this case of flat platesto be applied, for example by means of gluing, to the edges of the innersides of the shells.

In detail, the plates 14 a and 14 b can be glued either to just one ofthe shells or to both of them, and either to one edge of the shell or toboth edges.

The edge of each plate 14 a, 14 b projects from the edge of one of theshells in such a way that it can couple with the edge of the other shellforming the covering and be glued to it.

The invention was previously described with reference to some preferredforms of embodiment of the same.

However it is clear that the present is susceptible to severalvariations within the scope of the present invention, in the field ofthe technical equivalences.

1. A process for the production of a steering wheel for motor vehicles,comprising the steps of: providing a substantially circular-shaped metalcore (11); burying said metal core (11) inside a synthetic resin (12),thereby forming a steering wheel body; preparing a pair of outercovering shells (13 a, 13 b) by means of hot forming of compositeelements with a laminated structure, said shells (13 a, 13 b) having acomplementary shape and being suitable to be placed over said steeringwheel body and joined together along their edges; preparing a system(14) for connecting and fastening to each other said shells (13 a, 13b), said system being constituted by a thin element (14) that is fixedto the inner side of one (13 a) of said shells in such a way that bothedges of said thin element (14) protrude over the edges of said shell(13 a), whereby the surface of said thin element (14) protruding overthe edges of said shell (13 a) forms an area for fastening said thinelement (14) to the inner side of the other shell (13 b); and joiningsaid two shells (13 a, 13 b) together along their edges, thereby fixingsaid other shell (13 b) to the said protruding surface of said thinelement (14); and joining said two shells (13 a, 13 b) together alongtheir edges, thereby fixing each respective shell (13 a, 13 b) to thesaid protruding surface of said thin elements (14 a, 14 b).
 2. A processaccording to claim 1, wherein said shells (13 a, 13 b) are joinedtogether by glueing.